The electric actuator has been hitherto used, for example, as a means for transporting a workpiece. As shown in FIGS. 9 and 10, such an electric actuator comprises a lengthy frame 1 formed with an opening to function as a main actuator body, and a block-shaped electric motor 2 secured to one end of the frame 1. The electric actuator includes a ball screw 3 and a motor shaft of the electric motor 2 which are coaxially coupled to one another by using an unillustrated coupling member. A movable member 4 is fixed to an unillustrated nut member which is engaged with the ball screw 3.
Long grooves 5a, 5b, which are provided for attaching sensors, are formed on a side surface of the flame 1 along the longitudinal direction of the frame 1. The sensor 6 is installed to a predetermined portion of the long groove 5a, 5b. A lead wire 7, which is electrically connected to the sensor 6, is led into the long groove 5a, 5b. One end of the lead wire 7 is connected to an external equipment such as a controller. A detection signal, which is detected by the sensor 6, is inputted into the external equipment.
A part of the opening of the frame 1 is closed with a cover plate 8. Slits 9a, 9b are formed at the remaining portions which are not closed with the cover plate 8 (see FIG. 10). The slits 9a, 9b communicate with the outside, and they are formed along the axial direction of the frame 1.
In this arrangement, the nut member, which is engaged with the ball screw 3, is linearly displaced along the slits 9a, 9b in accordance with the driving action of the electric motor 2. Thus, the movable member 4, which is fixed to the nut member, is displaced in an integrated manner.
However, in the case of the electric actuator concerning the conventional technique described above, the slits 9a, 9b, which serve as the space for moving the nut member, are formed at the opening of the frame 1. Therefore, any dust or the like enters the inside of the frame 1 from the outside via the slits 9a, 9b, and it adheres to the ball screw 3. As a result, an inconvenience arises in that the driving force-transmitting function of the ball screw 3 is lowered, and it becomes impossible to allow the movable member 4 to make smooth reciprocating motion.
Further, for example, any maintenance work is performed, the following inconvenience arises. That is, an operator contacts with the lead wire 7 exposed from the long groove 5a, 5b to the outside, and the lead wire is hitched thereby. As a result, the position of the sensor 6 having been installed at the predetermined portion of the long groove 5a, 5b is deviated.
An object of the present invention is to provide an electric actuator which makes it possible to prevent the inside of the main actuator body from invasion of dust or the like so that any decrease in the driving force-transmitting function is avoided, and which makes it possible to avoid any positional deviation of the sensor, which would be otherwise caused by the stretching action effected on the lead wire.